Search found 2724 matches

by tomfid
Wed Aug 21, 2019 9:06 pm
Forum: Vensim
Topic: Integrating time step of optimization problem
Replies: 24
Views: 1390

Re: Integrating time step of optimization problem

I mentioned noise for the following reason. If the auction is structured so that bids reveal true marginal costs, and that information is disclosed, then everyone has a pretty good idea what the aggregate supply curve looks like. Therefore they can do a pretty good job of anticipating the clearing p...
by tomfid
Wed Aug 21, 2019 8:31 pm
Forum: Ventity
Topic: Many-to-Many Relationship Cohorts
Replies: 8
Views: 191

Re: Many-to-Many Relationship Cohorts

This is more like what you need. Note that I've replaced the Fleet's key attribute, FleetID, with a compound key consisting of Size and Type. That wasn't really necessary, and it slightly complicates the Cohort. It does make plots of fleet items a little easier to read.
VehicleCohorts4.zip
(19.97 KiB) Downloaded 6 times
by tomfid
Wed Aug 21, 2019 8:21 pm
Forum: Ventity
Topic: Many-to-Many Relationship Cohorts
Replies: 8
Views: 191

Re: Many-to-Many Relationship Cohorts

Also, you've deleted the "Head Cohort" attribute in the Fleet entity. That's needed to refer to the newest cohort of vehicles of a given size and type, so that sales can be inserted there.
by tomfid
Wed Aug 21, 2019 7:53 pm
Forum: Vensim
Topic: Integrating time step of optimization problem
Replies: 24
Views: 1390

Re: Integrating time step of optimization problem

It seems like this should result in an outcome much like a single clearing price, but with a little more noise. If I'm running unit X, I don't want to bid my marginal cost. I want to figure out where the market is likely to clear next period, and bid just below that. However, the price in the next p...
by tomfid
Wed Aug 21, 2019 7:38 pm
Forum: Vensim
Topic: Integrating time step of optimization problem
Replies: 24
Views: 1390

Re: Integrating time step of optimization problem

Ah ... so the problem is more game theoretic. Each plant has to choose a bid that maximizes profit, subject to everyone else doing the same. We know the bid has to lie above marginal cost, and below a price cap (set by regulator?). Is the capacity constraint loose, in the sense that they want to run...
by tomfid
Wed Aug 21, 2019 7:33 pm
Forum: Vensim
Topic: Integrating time step of optimization problem
Replies: 24
Views: 1390

Re: Integrating time step of optimization problem

Does your capacity constraint imply that A generates 100 to 300 or 0 ? That probably can't be done with the alloc functions. Not sure it could be done with FIND ZERO or even an LP either. It makes this more of a mixed integer programming problem, right?
by tomfid
Wed Aug 21, 2019 7:09 pm
Forum: Vensim
Topic: Integrating time step of optimization problem
Replies: 24
Views: 1390

Re: Integrating time step of optimization problem

Doesn't everyone who supplies > 0 get paid at the (single) market clearing price, rather than their bid price?
by tomfid
Wed Aug 21, 2019 7:00 pm
Forum: Ventity
Topic: Many-to-Many Relationship Cohorts
Replies: 8
Views: 191

Re: Many-to-Many Relationship Cohorts

Actually, that's not quite right - your cohorts need a separate ID. It's not sufficient to have Car Size|Engine Type|Fleet for the cohort key, because it's not unique. There will be multiple model years with the same attributes.
by tomfid
Wed Aug 21, 2019 6:57 pm
Forum: Ventity
Topic: Many-to-Many Relationship Cohorts
Replies: 8
Views: 191

Re: Many-to-Many Relationship Cohorts

I think you've nearly done it here - you just need to initialize the FMrelationship entity Car Size and Engine Type attributes in the Create Cohort action. This will be analogous to the Fleet initialization, i.e. you'd set Car Size = Invoker.HC Car Size. Generally the easy way to do this is to write...
by tomfid
Wed Aug 21, 2019 6:13 pm
Forum: Vensim
Topic: Integrating time step of optimization problem
Replies: 24
Views: 1390

Re: Integrating time step of optimization problem

The FIND ZERO example model in the Help system is already pretty close to what you need. I'll see if I have something better.

Have you explored the allocation functions? That would be an even easier solution.
by tomfid
Wed Aug 21, 2019 6:07 pm
Forum: Vensim
Topic: BUG: Mac Vensim 8 output windows have black text in dark mode
Replies: 5
Views: 128

Re: BUG: Mac Vensim 8 output windows have black text in dark mode

I'd favor the latter approach, because PLE is used so much for teaching. Having radically different appearances on different platforms is problematic.
by tomfid
Wed Aug 21, 2019 6:05 pm
Forum: Vensim
Topic: Working with Levels in Vensim
Replies: 2
Views: 83

Re: Working with Levels in Vensim

Levels can't literally reflect flows instantaneously - that would be a violation of causality. However, if your model is essentially running in discrete time, and you want end-of-period levels instead of start-of-period, you can use the Diff integration method (instead of Euler) to shift the reporti...
by tomfid
Tue Aug 20, 2019 2:23 pm
Forum: Vensim
Topic: Variables in text and sketch views
Replies: 3
Views: 89

Re: Variables in text and sketch views

If you're adding many, you can turn on the sketch varlist: https://www.vensim.com/documentation/sketchlayout.htm
by tomfid
Fri Aug 16, 2019 7:29 pm
Forum: Vensim
Topic: vensim .mdl extension applied to flight sim files
Replies: 7
Views: 138

Re: vensim .mdl extension applied to flight sim files

If your flight simulator is still choking on this somehow, my recommendation would be to re-associate the files with the flight simulator. Then you will have the reverse problem, that you won't be able to open a Vensim model via a double-click in Explorer. But you'll still be able to open models fro...
by tomfid
Wed Aug 14, 2019 8:36 pm
Forum: Vensim
Topic: vensim .mdl extension applied to flight sim files
Replies: 7
Views: 138

Re: vensim .mdl extension applied to flight sim files

Vensim does register for the mdl file time when installed, but on Windows the file type really has no effect on a program's access to a file. There's no "renaming" involved. So, I don't see how that could affect your simulator's performance. What was the specific symptom of the crash? Is there an er...
by tomfid
Tue Aug 13, 2019 6:51 pm
Forum: Vensim
Topic: New User (Graduate Engineering Student) Modeling/Software Issues with Real Time Experiment
Replies: 7
Views: 158

Re: New User (Graduate Engineering Student) Modeling/Software Issues with Real Time Experiment

I think there are still several problems here. 1. Units don't balance. This is an automatic disqualifier in my view. 2. I don't think area and strain can be independent. As long as density is constant, the volume of the sample will be conserved, so increasing strain decreases area, without integrati...
by tomfid
Mon Aug 12, 2019 9:21 pm
Forum: Vensim
Topic: Error: Variable not used in the model
Replies: 1
Views: 68

Re: Error: Variable not used in the model

The "not used" issue is a warning, not an error. You can suppress it by checking the "Supplementary" box in the equation editor for the two variables in question.

If the model won't run, something else more serious is wrong.
by tomfid
Mon Aug 12, 2019 1:55 pm
Forum: Vensim
Topic: Change the default legend in the custom graph tool
Replies: 2
Views: 72

Re: Change the default legend in the custom graph tool

1. Can't presently be done, but this tool will get an overhaul in a forthcoming release.
2. You could do this using the "Label" field, but you'd have to have one entry per subscript element shown, which would be a little cumbersome.
by tomfid
Thu Aug 08, 2019 7:52 pm
Forum: Vensim
Topic: New User (Graduate Engineering Student) Modeling/Software Issues with Real Time Experiment
Replies: 7
Views: 158

Re: New User (Graduate Engineering Student) Modeling/Software Issues with Real Time Experiment

I think what you have is correct, but you're violating the SD stock-flow conventions by introducing the stiffness parameter into the stock via an information arrow. If you want to follow conventions, Strain is a stock (as is) with a flow of Elongation, and elongation = force/area/stiffness. I don't ...
by tomfid
Thu Aug 08, 2019 1:30 pm
Forum: Vensim
Topic: New User (Graduate Engineering Student) Modeling/Software Issues with Real Time Experiment
Replies: 7
Views: 158

Re: New User (Graduate Engineering Student) Modeling/Software Issues with Real Time Experiment

I don't think you want to make the area a stock. It's a function of the elongation of the object.
by tomfid
Tue Aug 06, 2019 9:55 pm
Forum: Ventity
Topic: using Visualizer without shapes
Replies: 4
Views: 134

Re: using Visualizer without shapes

I should probably cook up an example. But the basic idea at present would be to assign a location (lat/lon) to each individual in the model, and then color the points according to infection status. Now that I think about it, points don't currently have dynamic size/shape/color, but that should be wo...
by tomfid
Tue Aug 06, 2019 9:52 pm
Forum: Ventity
Topic: using Visualizer without shapes
Replies: 4
Views: 134

Re: using Visualizer without shapes

Right.
by tomfid
Tue Aug 06, 2019 9:14 pm
Forum: Vensim
Topic: Is there an equation for counter in Vensim?
Replies: 2
Views: 120

Re: Is there an equation for counter in Vensim?

If you need a fixed window, you can use something like: avg input = x in window/tau x in window = INTEG( input - outflow, input*tau ) outflow = DELAY FIXED( input, tau, input ) tau = 3 The time scale tau needs to be an integer multiple of the time step for this to initialize correctly, though you co...
by tomfid
Tue Aug 06, 2019 9:11 pm
Forum: Vensim
Topic: Is there an equation for counter in Vensim?
Replies: 2
Views: 120

Re: Is there an equation for counter in Vensim?

An extremely simple implementation would be A = PR/SMOOTH(PR,smoothing time) smoothing time = 3 The SMOOTH function gives you an exponentially-weighted moving average of its input, which is often a good model of perception. A fixed window is typically not as good a model of perception, unless there'...